Acyclovir Dosing for Chickenpox Prophylaxis
For prophylaxis of chickenpox in susceptible individuals after exposure, the recommended dose of acyclovir is 20 mg/kg body weight (maximum 800 mg per dose) orally 4 times daily for 5-7 days, starting within 7-10 days of exposure to varicella-zoster virus. 1, 2
Prophylaxis Indications and Timing
- Acyclovir prophylaxis should be considered when varicella-zoster immune globulin (VZIG) is not available or more than 96 hours have passed since exposure 1
- Prophylactic treatment with oral acyclovir should be initiated within 7-10 days of exposure to chickenpox 1, 2
- The prophylactic course should continue for 5-7 days 1, 2
Dosing by Population
Children
- For children: 20 mg/kg body weight (maximum 800 mg per dose) orally 4 times daily for 5-7 days 2, 3
- For children under 45 kg: Some guidelines suggest 20 mg/kg body weight (maximum 400 mg per dose) orally 3-4 times daily 2
Adults and Adolescents
Special Populations
- For immunocompromised patients with hypogammaglobulinemia who are susceptible to VZV, prophylaxis with acyclovir is recommended if VZIG is not available 1
- Immunocompromised patients may require more aggressive prophylaxis and should be monitored closely 1
- For patients with congenital nephrotic syndrome exposed to chickenpox who are not immunized against VZV, prophylactic acyclovir (10 mg/kg four times a day for 7 days) is recommended 1
Clinical Considerations
- Acyclovir prophylaxis is not routinely indicated for healthy individuals after exposure to varicella 2
- The first-line option for post-exposure prophylaxis in high-risk individuals is varicella-zoster immune globulin (VZIG) administered within 96 hours of exposure 1
- Acyclovir prophylaxis should be considered as an alternative when VZIG is not available or when more than 96 hours have passed since exposure 1
Efficacy and Limitations
- Prophylactic acyclovir may reduce the severity of chickenpox symptoms but does not completely prevent infection 3, 5
- Acyclovir does not eradicate latent virus or affect subsequent risk, frequency, or severity of recurrences 2
- Antibody titers after infection in children receiving acyclovir do not differ substantially from those not receiving treatment 2, 6
Monitoring and Follow-up
- Monitor for potential side effects including nausea, vomiting, diarrhea, and headache 7
- Ensure adequate hydration during treatment 7
- Adjust dosing in patients with renal impairment 7
Remember that early initiation of prophylaxis is critical for effectiveness, as studies show diminishing benefits when treatment is delayed beyond the first 24 hours after rash onset in active infection 3, 5, 4.